How to repair stripped stud threads?

[BK911]

Tightening up nut for a master cylinder on a brake booster, and all of a sudden the nut was loose again.
Took it all apart and noticed the studs on the brake booster are chewed up.
I was thinking about filing down the remaining threads and tapping the stud to the next size down.
Then I read about loctite 660.
Looks like this might work if I apply, let dry, then thread?
Anybody use this stuff? Or something similar?

[javadog]

That’s one of those fasteners that I think is fairly critical. I would either replace the stud or replace the booster. You may have to remove the booster to replace the stud, I’ve got no idea what car we’re talking about here.

[John Rogers]

Not sure what you mean by tapping? You have two choices, first is to use an under sized nut, not the best since you are working with brakes here. Best solution is to pull out both studs and replace them. Use plenty of Kroil to break the metal bond loose.

[BK911]

Its on a '67 Cadillac.
Just bought the booster and MC and somehow stipped the threads already.
Its the one circled in red.
By tapping, I meant re-threading with a die.
Applying the liquid metal, loctite 660, JB weld, or similar, letting dry, then threading to the original thread.
Or sanding down whats left of the threads and thread to next size down.
The existing threads are metric at 10mm x 1.5. Next size down is 3/8 x 16. Not much smaller, but should be enough to get a good bite.
Next option is a new vacuum booster at ~$125.
I tried removing the stud but couldn't figure out how to do it and was afraid I was going to ruin the new booster. Are they pressed in or threaded? Double nut with some heat?

[Tobra]

How is it there are metric threads on a 1967 Caddy?

[fastfredracing]

Here is an idea for a rig. I bet the threads are only stripped at the bottom of the stud. Use a stack of washers, or larger nut to take up the space, then put the correct nut on the end of the threaded stud , where the threads are still good. If it holds tight, you are good to go !

[javadog]

Originally Posted by Tobra

How is it there are metric threads on a 1967 Caddy?

Part made in China.

Part made from poor quality Chinesium steel

[javadog]

Originally Posted by fastfredracing

Here is an idea for a rig. I bet the threads are only stripped at the bottom of the stud. Use a stack of washers, or larger nut to take up the space, then put the correct nut on the end of the threaded stud , where the threads are still good. If it holds tight, you are good to go !

That’s a good idea. It’s always helpful, if you post a picture of the actual part you’re asking about, hint hint...

[BK911]

Yup, parts made in China.
Took a few minutes to find the right Die, because I was trying all the metric stuff.
Tried the washer trick, no bueno.
The threads stripped because the proportioning valve plate was off by just a little, and was scraping the threads as I tightened it down.
So they are stripped from the beginning to about half way.
I will get a pic when I get home tonight.

[john70t]

Originally Posted by BK911

By tapping, I meant re-threading with a die.

Tapping would require re-threading the inside of the hole (female) and buying a new stud that matched .
A die would cut/clean up the outside of the existing threads (male).

Plan A. Trying to save the existing stud would be my first choice.
Plan B. Replace stud.
Plan C. Buying a new booster.

Make sure the tool is lined up at all times because it will want to walk around following the goobered part.
Go very slow with pressure and use oil.

It depends on how much thread is remaining and if the nut seats past the damage.
(The hack in me would zap a quick weld dot on top to keep it from loosening while pressing in turning, but that would be wrong.)

Originally Posted by BK911

Are they pressed in or threaded?

No idea here. They could even bolt from inside.

If using heat to remove the stud, that plastic vacuum connector should probably be removed first.
There is a rubber seal around the fulcrum plate and probably another one for the exit shaft next to the stud.
Use high and localized heat right at the base to melt the Locktite. Oxy/Acetylene or MAPP with a small welding tip.
Getting an exact new stud might be tedious depending on your schedule. McMaster-Carr will have them.

Might be easier to buy a new booster depending on time/money/tools.

[speeder]

What was wrong w the old booster? Was it bad?

[BK911]

Not sure if it was bad, but it was ~50 years old!
Brakes didn't work too well mostly because swollen rubber lines.
Decided to go all new.

[javadog]

Might want to put the old one back on if it was still working....

[GH85Carrera]

I would never use a POS Chinese brake part on any car I own.

I bet you can get the original one rebuilt and working, or find a new GM part.

[Tobra]

What Glen said

[wdfifteen]

Originally Posted by fastfredracing

Here is an idea for a rig. I bet the threads are only stripped at the bottom of the stud. Use a stack of washers, or larger nut to take up the space, then put the correct nut on the end of the threaded stud , where the threads are still good. If it holds tight, you are good to go !

You beat me to to it. But please use a stack of washers that fit as snug on the stud as you can get. Use metric washers if you need to. Don't hillbilly it up with a nut or sloppy washers.
Speaking of Appalachian Engineering, when I had a similar situation with an exhaust manifold nut on my old Tundra I snugged the nut up good and tight and then welded it on. (Not that I recommend that in your case)

[wdfifteen]

Originally Posted by GH85Carrera

I would never use a POS Chinese brake part on any car I own.

Then there is this. If it is so cheaply made that the mounting studs give out on assembly, what kind of material and workmanship can you expect from the rest of it?
Given that this is your brakes, I would get a genuine US made part if possible and pitch that (possible) POS.

[speeder]

Originally Posted by javadog

Might want to put the old one back on if it was still working....

Originally Posted by GH85Carrera

I would never use a POS Chinese brake part on any car I own.

I bet you can get the original one rebuilt and working, or find a new GM part.

Originally Posted by BK911

Not sure if it was bad, but it was ~50 years old!
Brakes didn't work too well mostly because swollen rubber lines.
Decided to go all new.

Doesn't matter if it's 150 years old, it's a lot better than the garbage parts you're installing. Brake boosters are either good or bad, there isn't a lot of in between. If it holds vacuum, it's good. Period.

Doesn't it tell you something when a component still works fine after 52 years? Like maybe it was well made?

[speeder]

Replacing the soft lines, (rubber), was absolutely a smart thing to do. Vital maintenance. But replacing hard parts like a MC and booster w massively inferior replacement parts is not very smart. Those are things that get replaced when they fail or show signs of impending failure. Never prophylacticly replace quality factory parts w Chinese crap.

[john70t]

Originally Posted by speeder

Brake boosters are either good or bad, there isn't a lot of in between. If it holds vacuum, it's good. Period.

Stick a MityVac gauge on the vacuum connector of the old one and pump it up -25lbs and wait.
If it holds internal negative pressure, i.e. vacuum, the old rubber seals are there.
(for now)

The rod spring tension with the shaft lubrication will still be unknown.
It should slide and return by pushing on it.